I know the feeling. Been there, done that.
It's always better to get them to agree with you, before you proceed to purchase your MBP. If later, for some reason you have to endure any hardship, they will be willing to help you.
You should make them convince themselves that you need your MBP, instead of just nagging about it. It may seem hard to do, but it's possible, and works for the best.
Well, I didn't talked about them yet. I've dropped a few rimes that I wanted a MacBook pro, but I never told them how much it would cost. I've subtely told them when I was looking in some pc folders from 1200-1800 that those were bad leptons 'cause somthing was always wrong etc.
Did you looked at my 6 point list some posts ago?
If I told them that, and let them show the calculations with an other pc laptop, do you think they will let me buy one? 'cause it looks impossible to me